For example, a wiring substrate installed in an electrical distribution box of a vehicle uses the wiring substrate configured to dispose a metal plate (soaking plate or heat dissipation plate) in an intermediate layer of the wiring substrate in order to avoid a local increase in temperature by heat generation of an electronic component (for example, see PTL 1). By using such a metal plate, the heat generated in the electronic component is diffused in the whole wiring substrate and thus a heat dissipation effect is promoted, so that damage to a circuit pattern and the electronic component by the local increase in temperature can be prevented.
FIGS. 10 and 11 are explanatory diagrams showing a configuration of a related wiring substrate 110, and FIG. 10 shows a surface layer and FIG. 11 shows an intermediate layer (that is, an inside layer excluding the surface layer), respectively. As shown in FIG. 11, a metal plate 111 having conductivity is disposed in substantially the center of the intermediate layer of the wiring substrate 110. Also, a plurality of protruding terminals 112 (12 pieces in the drawings) having rectangular shapes are respectively disposed in the left lateral side part and the right lateral side part of the wiring substrate 110, and a part of each of the protruding terminals 112 protrudes toward the outside of the wiring substrate 110. Then, when a connector (not shown) is connected to the wiring substrate 110, this protruding portion can be used as a terminal for connector connection.
Also, as shown in FIG. 10, a prepreg 131, which is an insulating material, is disposed on a face of the wiring substrate 110 and the surface layer is formed. On this surface layer, various electronic components 115 are installed and a circuit pattern 114 is cabled. Further, in order to connect the circuit pattern 114 disposed in the surface layer to the protruding terminals 112 disposed in the intermediate layer, through holes 113 are bored in at least one of the plural protruding terminals 112 (see FIG. 11). That is, the protruding terminals 112 can be electrically connected to the circuit pattern 114 via the conductive through holes 113.
Also, for example, in the case of electrically connecting three through holes 113-1, 113-2, 113-3 shown in the upper left of FIG. 10, it is necessary to provide circuit patterns 114-1, 114-2 for making connection between each of the through holes 113-1, 113-2, 113-3 on the surface layer of the wiring substrate 110. The circuit patterns 114 formed on the surface layer of the wiring substrate 110 increase and a problem of reducing space for arranging the electronic components by the increased circuit patterns arises.